1. Department of Materials Science and Engineering, University of California 1 , Los Angeles, California 90095, USA
2. California NanoSystems Institute, University of California 2 , Los Angeles, California 90095, USA
3. KLA Instruments Group 3 , West Covina, California 91791, USA
4. Materials Research and Education Center, Department of Mechanical Engineering, Auburn University 4 , Auburn, Alabama 36849, USA